The present studies examine the breadth and magnitude of neutralizing antibody responses in small animals and rhesus monkeys after various immunization regimens. Using a standardized multi-tier panel of reference Env pseudoviruses for neutralizing antibody assessment, we show that both protein immunization, and DNA prime, rAd boost immunization, can generate high antibody titers. Ongoing studies are evaluating novel immunogens based on structure-based information from studies of the HIV-1 envelope glycoprotein.